Wireless IP phones have started to be used under various environments, such as corporations and private houses, utilizing platforms promoted according to the popularization of wireless LAN of these days. In a communication system using the wireless IP phones which have started to spread in corporations, there is a system having a group incoming call function for calling a plurality of terminal devices in response to a single request of call connection, and assigning a required communication band to a single terminal device which answered the call to establish call connection.
In Japanese Patent No. 2859210, a communication system having a group incoming call function for assigning one of telephone call channels of a base station to carry out a broadcast call to a plurality of wireless mobile stations is proposed.
However, the conventional communication system described in Japanese Patent No. 2859210 has a problem in which it carries out band securing for assigning a predetermined communication band set in advance for the request of call connection, and after establishing the call connection, it carries out a telephone call by establishing the call connection in the reserved communication band, and therefore, the assigned communication band is not always appropriate. Because a communication situation changes in the wireless IP phone according to the communication environment between the terminal device and the base station device used as an access point, not all of the communication situation of the plurality of terminal devices to be targets of the group incoming call are the same. For example, if a communication environment is bad and call connection is established for a terminal device which requires a communication band wider than a communication band set in advance, situations, such as communication quality deterioration, audio quality degradation, and abnormal cutting of the call connection, occur. On the other hand, for example, if a communication environment is good and call connection is established for a terminal device which can communicate in a communication band narrower than the communication band set in advance, the communication efficiency as the whole system gets worse because the communication band is occupied more than needed.